1. Field of the Invention
The present invention relates generally to a microprocessor and a video/sound processing system, and more particularly, to a technology that provides high-level protection for the content of media at low cost.
2. Description of Related Art
Currently, devices that handle video, sound, and other content are provided with a microprocessor or a dedicated LSI for playing back video and/or sound information. Video, sound, and other data (hereinafter called “content”) are often stored on such physical media as optical disks and such magnetic recording devices as hard disk drives (HDD). In recent years, most of the video and voice information stored on optical disks and magnetic recording devices is treated with encryption or the like using a special method for the purpose of copyright protection. Since the content stored in recording devices like those just mentioned has been treated for protection and security, persons who might attempt to misuse the stored data and play it back on another device will generally be unable to easily break the security. However, if an analytical hint is available, it is possible for the security to be broken easily by conducting data processing on a computer.
Information that constitutes an analytical hint exists in the unit where the data is ultimately processed, i.e., in the vicinity of the microprocessor or dedicated LSI. That is where the encrypted information is decrypted and translated into the original information. Much of the decrypted and converted information is stored in a memory, e.g., a random access memory (RAM), connected to the processor or dedicated LSI that executes the data processing. In such a case, an analytical hint can be obtained by using a test device to measure the signal of the RAM itself and analyzing the data. The information from the analysis can then be used as a starting point for breaking the security.
Conventional technologies for handling this issue have included combining the processor and the memory into one chip in order to conceal the bus of the memory and silk printing a different model number on the IC package so that the identity of the processor will be unknown.
Meanwhile, a disclosed conventional method of resisting illicit decryption of secret information is a technology in which a means is provided for randomly changing secret information when writing to a volatile memory that stores secret information after it has been translated, the converting means converts and stores the secret information in different places each time the secret information is written to the volatile memory and also in different places of each electronic device in which the technology is used. (See Japan Patent Office Publication (Kokai) HEI-11-45212 (FIG. 1).)
In another disclosed technology, the bus interface unit inside a microprocessor is provided with an address translating means that converts virtual addresses into physical addresses and a memory reading means that reads the content corresponding to physical addresses designated by a memory external to the microprocessor. An instruction TLB stores a table that includes an address conversion rule and one or more entries having encryption attribute information in ranges designated by the virtual addresses. (See Japan Patent Office Publication (Kokai) 2001-230770 (FIG. 5).)
The conventional methods just described require specialized components to be manufactured and make it extremely difficult to reduce costs. In most cases, general-purpose memories are used in order to reduce the cost of the system. However, the use of general-purpose memories is a problem because it is possible for the signal line connected to the memory and the function of that signal line to be readily ascertained.